1. Field of the Invention
The present invention relates to a decision feedback equalizer used for canceling CW (continuous wave) interference.
2. Description of the Related Art
As described in an article "Rejection of CW Interference in QPSK Systems Using Decision-Feedback Filters", L. Li and L. B. Milstein, a, IEEE Transactions on Communications, Vol. COM-31, No. 4, April 1983, decision feedback equalizers include a forward transversal filter whose reference tap is located at the center of its tapped delay line for compensating for the deleterious effect of CW interference on the quality of transmitted signal, and a backward filter for canceling intersymbol interference. While satisfactory for operation during the presence of CW interference, a sudden absence of the CW interference causes the tap-gain coefficients of the forward filter to remain at the value which they attained at the time just prior to the disappearance of the CW interference. Since such conditions persist for a certain length of time, an increase in bit error rate results. Moreover, if new CW interference of different frequency occurs in the absence of the previous CW interference, the equalizer encounters instability and the tap-gain coefficients of both forward and backward filters diverge out of control.